Storage space is often limited. Stacking of boxes and other containers has provided a solution for some storage limitations, but not for fields of use where it is advantageous or desirable to frequently use the stored contents, especially in a location somewhat remote from the storage place. For example, it is advantageous and desirable for those involved in sports using balls to have convenient access to game balls during practice. However, often storage space is limited for balls and equipment used in exercise and team sports. Moreover, known collapsible bins are relatively immobile and/or too flimsy to be practical; and none provide for mobile storage.